common/AMWD.Common/Packing/Tar/Utils/TarHeader.cs

using System;
using System.Linq;
using System.Net;
using System.Text;
using AMWD.Common.Packing.Tar.Interfaces;

namespace AMWD.Common.Packing.Tar.Utils
{
	internal class TarHeader : ITarHeader
	{
		private static readonly byte[] _spaces = Encoding.ASCII.GetBytes("        ");
		private readonly byte[] _buffer = new byte[512];

		private string _fileName;
		private long _headerChecksum;

		public TarHeader()
		{
			// Default values
			Mode = 511; // 0777 dec
			UserId = 61; // 101 dec
			GroupId = 61; // 101 dec
		}

		public EntryType EntryType { get; set; }

		public virtual string FileName
		{
			get => _fileName.Replace("\0", string.Empty);
			set
			{
				if (value.Length > 100)
					throw new TarException("A file name can not be more than 100 chars long");

				_fileName = value;
			}
		}

		public int Mode { get; set; }

		public string ModeString
			=> Convert.ToString(Mode, 8).PadLeft(7, '0');

		public int UserId { get; set; }

		public virtual string UserName
		{
			get => UserId.ToString();
			set => UserId = int.Parse(value);
		}

		public string UserIdString
			=> Convert.ToString(UserId, 8).PadLeft(7, '0');

		public int GroupId { get; set; }

		public virtual string GroupName
		{
			get => GroupId.ToString();
			set => GroupId = int.Parse(value);
		}

		public string GroupIdString
			=> Convert.ToString(GroupId, 8).PadLeft(7, '0');

		public long SizeInBytes { get; set; }

		public string SizeString
			=> Convert.ToString(SizeInBytes, 8).PadLeft(11, '0');

		public DateTime LastModification { get; set; }

		public string LastModificationString
		{
			get
			{
				long unixTime = ((DateTimeOffset)DateTime.SpecifyKind(LastModification, DateTimeKind.Utc)).ToUnixTimeSeconds();
				return Convert.ToString(unixTime, 8).PadLeft(11, '0');
			}
		}

		public string HeaderChecksumString
			=> Convert.ToString(_headerChecksum, 8).PadLeft(6, '0');

		public virtual int HeaderSize => 512;

		public byte[] GetBytes() => _buffer.ToArray();

		public virtual bool UpdateHeaderFromBytes()
		{
			FileName = Encoding.ASCII.GetString(_buffer, 0, 100);

			// Thanks to Shasha Alperocivh. Trimming nulls.
			Mode = Convert.ToInt32(Encoding.ASCII.GetString(_buffer, 100, 7).Trim(), 8);
			UserId = Convert.ToInt32(Encoding.ASCII.GetString(_buffer, 108, 7).Trim(), 8);
			GroupId = Convert.ToInt32(Encoding.ASCII.GetString(_buffer, 116, 7).Trim(), 8);

			EntryType = (EntryType)_buffer[156];

			if ((_buffer[124] & 0x80) == 0x80) // if size in binary
			{
				long sizeBigEndian = BitConverter.ToInt64(_buffer, 0x80);
				SizeInBytes = IPAddress.NetworkToHostOrder(sizeBigEndian);
			}
			else
			{
				SizeInBytes = Convert.ToInt64(Encoding.ASCII.GetString(_buffer, 124, 11), 8);
			}
			long unixTimeStamp = Convert.ToInt64(Encoding.ASCII.GetString(_buffer, 136, 11), 8);
			LastModification = DateTimeOffset.FromUnixTimeSeconds(unixTimeStamp).DateTime;

			int storedChecksum = Convert.ToInt32(Encoding.ASCII.GetString(_buffer, 148, 6));
			RecalculateChecksum(_buffer);
			if (storedChecksum == _headerChecksum)
				return true;

			RecalculateAltChecksum(_buffer);
			return storedChecksum == _headerChecksum;
		}

		private void RecalculateAltChecksum(byte[] buf)
		{
			_spaces.CopyTo(buf, 148);
			_headerChecksum = 0;
			foreach (byte b in buf)
			{
				if ((b & 0x80) == 0x80)
				{
					_headerChecksum -= b ^ 0x80;
				}
				else
				{
					_headerChecksum += b;
				}
			}
		}

		public virtual byte[] GetHeaderValue()
		{
			// Clean old values
			Array.Clear(_buffer, 0, _buffer.Length);

			if (string.IsNullOrEmpty(FileName))
				throw new TarException("FileName can not be empty.");

			if (FileName.Length >= 100)
				throw new TarException("FileName is too long. It must be less than 100 bytes.");

			// Fill header
			Encoding.ASCII.GetBytes(FileName.PadRight(100, '\0')).CopyTo(_buffer, 0);
			Encoding.ASCII.GetBytes(ModeString).CopyTo(_buffer, 100);
			Encoding.ASCII.GetBytes(UserIdString).CopyTo(_buffer, 108);
			Encoding.ASCII.GetBytes(GroupIdString).CopyTo(_buffer, 116);
			Encoding.ASCII.GetBytes(SizeString).CopyTo(_buffer, 124);
			Encoding.ASCII.GetBytes(LastModificationString).CopyTo(_buffer, 136);

			//            buffer[156] = 20;
			_buffer[156] = ((byte)EntryType);

			RecalculateChecksum(_buffer);

			// Write checksum
			Encoding.ASCII.GetBytes(HeaderChecksumString).CopyTo(_buffer, 148);

			return _buffer;
		}

		protected virtual void RecalculateChecksum(byte[] buf)
		{
			// Set default value for checksum. That is 8 spaces.
			_spaces.CopyTo(buf, 148);

			// Calculate checksum
			_headerChecksum = 0;
			foreach (byte b in buf)
				_headerChecksum += b;
		}
	}
}